Google Talk is an instant-messaging service from Google that you can use to send messages, files, or e-mail or make VoIP calls to people on your contact list. Since Google Talk is based on an open protocol (XMPP), it can be used to connect to any device that supports this protocol; this currently means Windows, Android, and BlackBerry devices, although other clients are bound to appear soon.
Google Talk reads your Gmail contact list, and the tight integration between Google Talk and Gmail allows you to send IMs to contacts in your Gmail account. Any chat conversations you have through Google Talk are saved and searchable by default. Offline messages are supported. The Google Talk interface is clean and easy to work with, and the application's integration with other Google tools is clean and easy, too.
Google Talk is a free download intended to compete with a host of other applications that offer similar capabilities. By integrating with Gmail and other apps, though, Google Talk has an edge, increased by its support of non-Windows clients. The application is small and fast, and we have encountered no problems in several years of using it.